1. Field of the Invention
The present invention relates to methods and apparatuses for driving liquid crystal display (LCD) panels. More particularly, the present invention relates to a method and an apparatus for driving an LCD panel that is capable of displaying moving pictures to increased brightness levels.
2. Description of the Related Art
Generally, liquid crystal display (LCD) devices display pictures by adjusting light transmittance characteristics of liquid crystal cell array in accordance with externally applied video signals. Active matrix type LCD devices are capable of displaying moving pictures. Accordingly, active matrix type LCD devices typically include switching devices such as thin film transistors (TFTs) arranged within each liquid crystal cell.
Depending on the response speed of liquid crystal material provided within each liquid crystal cell, a motion blurring phenomenon, wherein images are ambiguously displayed, and a tailing phenomenon, wherein contours of moving images may appear during operation of the LCD device. When the response speed of the liquid crystal is faster than a typical frame period (i.e., 16.7 ms), the appearance of moving images cannot be prevented from deteriorating.
Cathode ray tubes (CRTs) are impulse-type display devices that display images only momentarily. Accordingly, CRTs do not maintain data signals throughout an entire frame period but can display moving images while minimizing the motion blurring and tailing phenomena.
FIG. 1 illustrates impulse characteristics of related art cathode ray tubes.
Referring to FIG. 1, individual pixels of a related art CRT, each comprised of fluorescent material, radiate light for only a fraction of a frame period of the CRT (i.e., 16.7 ms) while remaining dark during the remainder of the frame period. Accordingly, individual pixels of the CRT display data for only a fraction of a frame period, thereby enabling CRTs to display moving images with an acceptable level of clarity.
FIG. 2 illustrates data voltage maintaining characteristics of related art liquid crystal display devices.
Referring to FIG. 2, and contrary to related art CRTs, individual pixels of related art LCD devices display images for the duration of the entire frame period. Accordingly, individual pixels maintain data throughout the frame period. Due to the aforementioned maintaining characteristic of related art LCD devices, the clarity to which moving images are displayed becomes deteriorated via the aforementioned motion blurring and tailing phenomena.
FIG. 3 illustrates a perspective view of a related art scanning backlight blinking system.
In order to minimize the degree to which the clarity of moving images are displayed by LCD devices is deteriorated, a related art scanning backlight blinking system has been proposed. Accordingly, the related art scanning backlight blinking system generally includes a backlight unit having first to fifth lamps 10a to 10e. Accordingly, the backlight unit radiates light to a LCD panel 1 by sequentially turning the plurality of lamps 10a to 10e on and off in accordance with data signals applied to the LCD panel 1.
Referring still to FIG. 3, when a center region of the LCD panel 1 transmits light emitted by a turned-on third lamp 10c, regions of the LCD panel 1 other than the center region do not transmit light because the first, second, fourth, and fifth lamps 10a, 10b, 10d, and 10e, are turned off. Moreover, the of the LCD panel 1 regions other than the center region remain dark while data signals while data signals are maintained within the liquid crystal cells arranged within those regions.
FIG. 4 illustrates impulse characteristics of a related art liquid crystal display device driven by a related art scanning backlight blinking system.
Referring to FIG. 4, and when the plurality of lamps 10a to 10e are sequentially are turned-on and off, the individual regions of the LCD panel 1 transmit light during a fraction of frame period of the LCD panel 1 (i.e., 16.7 ms) and remain dark during the remainder of the frame period. While the aforementioned related art scanning backlight blinking system can improve the clarity with which moving images are displayed by LCD panels 1, the scanning backlight blinking system undesirably causes regions of the LCD panel to remain for excessively long periods of time during any given frame period of the LCD panel. As a result, implementation of the scanning backlight blinking system tends to reduce the overall brightness to which images are displayed by the LCD panel 1 by as much as 50%.
FIG. 5 illustrates a liquid crystal display panel driven according to a related art field sequential driving system.
Referring to FIG. 5, the related art field sequential driving system (FS driving system) can be used to overcome problems associated with the scanning backlight blinking system. According to the FS driving system, a color filter typically formed on an upper substrate 20 of an LCD panel is removed and a backlight unit, including red, green, and blue light sources 32R, 32G, and 32B, is provided beneath a lower substrate 30 of the LCD panel.
FIG. 6 illustrates an operation of the related art FS driving system shown in FIG. 5 applied to a liquid crystal display panel.
Referring to FIG. 6, upon operation of the related art FS driving system, the red, green, and blue light sources 32R, 32G, and 32B are sequentially turned on and off in accordance with data signals charged to liquid crystal cells of the LCD panel. More specifically, during a scanning period (i.e., when gate pulses are applied to TFTs within liquid crystal cells), red data signals are charged to liquid crystal cells. Next, voltages corresponding to the charged red data signals are applied to liquid crystal material arranged within the liquid crystal cells. In response to the applied voltages, an orientation of molecules within the liquid crystal material becomes altered, thereby effecting an alteration in the light transmittance characteristics of the liquid crystal cell. Accordingly, time required to fully alter the light transmittance characteristics of the liquid crystal cell depends upon how quickly the molecular orientation of the liquid crystal material fully responds to the applied voltage (i.e., the response time of the liquid crystal material). Subsequently, the FS driving system turns the red light source 32R on to emit red light. Accordingly, the aforementioned FS steps of charging data signals, effecting a liquid crystal response, and turning on/off the red light source 32R occurs during a sub-frame period constituting ⅓ of the total frame period of the LCD panel (i.e., 5.56 ms). After the red light sourced 32R emits the red light, the aforementioned FS steps are sequentially repeated for green and blue data and colors.
Because data voltages specific to R, G, and B colors are applied to the LCD panel sub-frame periods one-third as long as a single frame period, benefits of the aforementioned related art FS driving method cannot be fully realized in certain types of LCD panels. More specifically, response times of TN mode LCD panels are generally longer than one frame period. Since the related art FS driving method requires that frame periods be sub-divided into sub-frame periods 5.56 ms in duration, liquid crystal molecules cannot fully respond to applied voltages, thereby preventing light transmittance characteristics of liquid crystal cells within the TN mode LCD panel from being fully altered. Accordingly, light emitted by light sources is transmitted by liquid crystal cells of TN mode LCD panels at a less than maximal intensity. Accordingly, when driven according to the aforementioned related art FS driving system, TN mode LCD panels undesirably display images at reduced brightness levels.
In view of the discussion above, benefits of the related art FS driving system can only be fully realized when applied to LCD panels having relatively fast response times (e.g., OCB or FLC mode LCD panels). Moreover, the related art FS driving system is difficult to integrate with LCD panels having high resolutions (e.g., VGA or greater) because high resolution LCD panels typically include liquid crystal cells that are formed using amorphous-type TFTs. Amorphous-type TFTs have a relatively low charge mobility, wherein the charge mobility of TFTs within liquid crystal cells affects the speed with which voltages may be applied to liquid crystal material.